Orthopedic hardware that is inserted in an intramedullary manner has become an increasingly useful aid in treating fractures of long bones (e.g. the femur or tibia). In a typical application, an interlocking rod or bar, commonly referred to as a "nail," is inserted into a femur and transverse screws or pins are used to fix the rod in place in the bone. These screws or pins are screwed or otherwise inserted from the outside of the limb or other body part through the adjacent bone wall into distal and transverse screw holes in the locking rod.
The use of such locking screws to ensure that the rod is fixed firmly in place has extended the range of such orthopedic aids and appliances well beyond that of the original locking rods without such transverse screws. However, the problem of properly inserting the screws from the outside of the limb is a different one. In this regard, it is noted that such locking rods are long enough that the rods will bend when installed and thus locking or positioning devices which are aligned or centered based on a reference taken from the top of the rod have been ineffective in precisely locating the transverse screw holes. It will be understood that the locking screws or pins must be precisely located so that the load on the limb involved is transmitted, during healing, through the transverse screws or pins and the associated locking rod and not through the broken portion of the bone.
One method that is capable of providing precise locating of the transverse distal holes in locking rods uses x-rays. However, long periods of x-ray exposure are required and the need to move the x-ray equipment into and out of position to check the screw or pin location means that there is a risk of a loss of alignment each time that the equipment is moved. As a consequence, the positioning of such locking screws or pins is typically the most time consuming and difficult portion of the overall rod implantation procedure.
In addition to x-rays, a number of different approaches have been taken in an attempt to find a safe, effective and rapid way of inserting transverse locking screws and pins into locking rods. Reference is made to U.S. Pat. No. 5,049,151 (Durham et al), U.S. Pat. No. 5,514,145 (Durham et al) and U.S. Pat. No. 5,707,375 (Durham et al) for a further discussion of these prior art approaches. A further approach involves a computer driven image of stacked magnetic coils which sense a magnetic field. One serious limitation of the latter approach concerns the fact that most locking rod systems will not accept a magnet that is placed at the screw hole.
As described therein, the systems disclosed in the above-mentioned U.S. Pat. Nos. 5,049,151, 5,514,145 and 5,707,375 involve the use of a pivotable magnetic positioning device in positioning a guide wire or pin over which a cannulated drill is passed so as to then permit the drill to drill a hole through the bone in alignment with the screw hole after the locating magnet is removed from the rod. Although the devices and methods disclosed in these patents represent important advances in the art, the requirement for such a guide wire or pin complicates the procedure.